MooX::Struct - make simple lightweight record-like structures that make sounds like cows
use MooX::Struct
Point => [ 'x', 'y' ],
Point3D => [ -extends => ['Point'], 'z' ],
;
my $origin = Point3D->new( x => 0, y => 0, z => 0 );
# or...
my $origin = Point3D[ 0, 0, 0 ];
MooX::Struct allows you to create cheap struct-like classes for your data
using Moo.
While similar in spirit to the MooseX::Struct manpage and the Class::Struct manpage,
MooX::Struct has a somewhat different usage pattern. Rather than providing
you with a struct keyword which can be used to define structs, you
define all the structs as part of the use statement. This means they
happen at compile time.
A struct is just an ``anonymous'' Moo class. MooX::Struct creates this class
for you, and installs a lexical alias for it in your namespace. Thus your
module can create a ``Point3D'' struct, and some other module can too, and
they won't interfere with each other. All struct classes inherit from
MooX::Struct.
Arguments for MooX::Struct are key-value pairs, where keys are the struct
names, and values are arrayrefs.
use MooX::Struct
Person => [qw/ name address /],
Company => [qw/ name address registration_number /];
The elements in the array are the attributes for the struct (which will be
created as read-only attributes), however certain array elements are treated
specially.
-
As per the example in the SYNOPSIS,
-extends introduces a list of
parent classes for the struct. If not specified, then classes inherit from
MooX::Struct itself.
Structs can inherit from other structs, or from normal classes. If inheriting
from another struct, then you must define both in the same use statement.
Inheriting from a non-struct class is discouraged.
# Not like this.
use MooX::Struct Point => [ 'x', 'y' ];
use MooX::Struct Point3D => [ -extends => ['Point'], 'z' ];
# Like this.
use MooX::Struct
Point => [ 'x', 'y' ],
Point3D => [ -extends => ['Point'], 'z' ],
;
-
Similarly
-with consumes a list of roles.
-
If an attribute name is followed by a coderef, this is installed as a
method instead.
use MooX::Struct
Person => [
qw( name age sex ),
greet => sub {
my $self = shift;
CORE::say "Hello ", $self->name;
},
];
But if you're defining methods for your structs, then you've possibly missed
the point of them.
-
If an attribute name is followed by an arrayref, these are used to set the
options for the attribute. For example:
use MooX::Struct
Person => [ name => [ is => 'ro', required => 1 ] ];
Using the init_arg option would probably break stuff. Don't do that.
-
Attribute names may be ``decorated'' with prefix and postfix ``sigils''. The prefix
sigils of
@ and % specify that the attribute isa arrayref or
hashref respectively. (Blessed arrayrefs and hashrefs are accepted; as are
objects which overload @{} and %{}.) The prefix sigil $
specifies that the attribute value must not be an unblessed arrayref or hashref.
The prefix sigil + indicates the attribute is a number, and provides
a default value of 0, unless the attribute is required. The postfix sigil
! specifies that the attribute is required.
use MooX::Struct
Person => [qw( $name! @children )];
Person->new(); # dies, name is required
Person->new( # dies, children should be arrayref
name => 'Bob',
children => 2,
);
Prior to the key-value list, some additional flags can be given. These begin
with hyphens. The flag -rw indicates that attributes should be
read-write rather than read-only.
use MooX::Struct -rw,
Person => [
qw( name age sex ),
greet => sub {
my $self = shift;
CORE::say "Hello ", $self->name;
},
];
The -retain flag can be used to indicate that MooX::Struct should
not use namespace::clean to enforce lexicalness on your struct class
aliases.
Flags -trace and -deparse may be of use debugging.
There are two supported methods of instatiating structs. You can use a
traditional class-like constructor with named parameters:
my $point = Point->new( x => 1, y => 2 );
Or you can use the abbreviated syntax with positional parameters:
my $point = Point[ 1, 2 ];
If you know about Moo and peek around in the source code for this module,
then I'm sure you can figure out additional ways to instantiate them, but
the above are the only supported two.
When inheritance or roles have been used, it might not always be clear what
order the positional parameters come in (though see the documentation for the
FIELDS below), so the traditional class-like style may be preferred.
Structs are objects and thus have methods. You can define your own methods
as described above. MooX::Struct's built-in methods will always obey the
convention of being in ALL CAPS (except in the case of _data_printer).
By using lower-case letters to name your own methods, you can avoid
naming collisions.
The following methods are currently defined. Additionally all the standard
Perl (isa, can, etc) and Moo (new, does, etc) methods are
available.
- OBJECT_ID
-
Returns a unique identifier for the object.
May only be called as an instance method.
- FIELDS
-
Returns a list of fields associated with the object. For the
Point3D struct
in the SYNPOSIS, this would be 'x', 'y', 'z'.
The order the fields are returned in is equal to the order they must be supplied
for the positional constructor.
Attributes inherited from roles, or from non-struct base classes are not included
in FIELDS, and thus cannot be used in the positional constructor.
May be called as an instance or class method.
- TYPE
-
Returns the type name of the struct, e.g.
'Point3D'.
May be called as an instance or class method.
- CLASSNAME
-
Returns the internally used package name for the struct, e.g.
'MooX::Struct::__ANON__::0007'. Pretty rare you'd want to see this.
May be called as an instance or class method.
- TYPE_TINY
-
Returns a the Type::Tiny manpage type constraint corresponding to the CLASSNAME,
suitable for a Moose/Moo
isa.
package Foo {
use Moo;
use MooX::Struct Bar => [qw( $name )];
has left_bar => (is => 'rw', isa => Bar->TYPE_TINY, coerce => 1);
has right_bar => (is => 'rw', isa => Bar->TYPE_TINY, coerce => 1);
...;
}
May be called as an instance or class method.
- TO_HASH
-
Returns a reference to an unblessed hash where the object's fields are the
keys and the object's values are the hash values.
May only be called as an instance method.
- TO_ARRAY
-
Returns a reference to an unblessed array where the object's values are the
array items, in the same order as listed by
FIELDS.
May only be called as an instance method.
- TO_STRING
-
Joins
TO_ARRAY with whitespace. This is not necessarily a brilliant
stringification, but easy enough to overload:
use MooX::Struct
Point => [
qw( x y ),
TO_STRING => sub {
sprintf "(%d, %d)"), $_[0]->x, $_[0]->y;
},
]
;
May only be called as an instance method.
- CLONE
-
Creates a shallow clone of the object.
May only be called as an instance method.
- EXTEND
-
An exverimental feature.
Extend a class or object with additional attributes, methods, etc. This method
takes almost all the same arguments as use MooX::Struct, albeit with some
slight differences.
use MooX::Struct Point => [qw/ +x +y /];
my $point = Point[2, 3];
$point->EXTEND(-rw, q/+z/); # extend an object
$point->can('z'); # true
my $new_class = Point->EXTEND('+z'); # extend a class
my $point_3d = $new_class->new( x => 1, y => 2, z => 3 );
$point_3d->TYPE; # Point !
my $point_4d = $new_class->EXTEND(\"Point4D", '+t');
$point_4d->TYPE; # Point4D
my $origin = Point[]->EXTEND(-with => [qw/ Math::Role::Origin /]);
This feature has been included mostly because it's easy to implement on top
of the existing code for processing use MooX::Struct. Some subsets of
this functionality are sane, such as the ability to add traits to an object.
Others (like the ability to add a new uninitialized, read-only attribute to
an existing object) are less sensible.
May be called as an instance or class method.
- BUILDARGS
-
Moo internal fu.
- _data_printer
-
Automatic pretty printing with the Data::Printer manpage.
use Data::Printer;
use MooX::Struct Point => [qw/ +x +y /];
my $origin = Point[];
p $origin;
Use Data::Printer 0.36 or above please.
With the exception of FIELDS and TYPE, any of these can be overridden
using the standard way of specifying methods for structs.
MooX::Struct overloads stringification and array dereferencing. Objects always
evaluate to true in a boolean context. (Even if they stringify to the empty
string.)
Because you only get an alias for the struct class, you need to be careful
with some idioms:
my $point = Point3D->new(x => 1, y => 2, z => 3);
$point->isa("Point3D"); # false!
$point->isa( Point3D ); # true
my %args = (...);
my $class = exists $args{z} ? "Point3D" : "Point"; # wrong!
$class->new(%args);
my $class = exists $args{z} ? Point3D : Point ; # right
$class->new(%args);
Please report any bugs to
http://rt.cpan.org/Dist/Display.html.
Moo, the MooX::Struct::Util manpage, the MooseX::Struct manpage, the Class::Struct manpage.
Toby Inkster <tobyink@cpan.org>.
This software is copyright (c) 2012-2013, 2017-2018 by Toby Inkster.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.
THIS PACKAGE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
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